递归
private static int find(Comparable[] arr, int l, int r, Comparable target){
if(l > r) return -1;
int mid = (r-l)/2 + l;
if(arr[mid].compareTo(target) == 0)
return mid;
else if(arr[mid].compareTo(target) > 0)
return find(arr, l, mid-1, target);
else
return find(arr, mid+1, r, target);
}
public static int find(Comparable[] arr, Comparable target){
return find(arr, 0, arr.length-1, target);
}private static int find(Comparable[] arr,